diff --git a/builder/virtualbox/iso/builder_test.go b/builder/virtualbox/iso/builder_test.go
index 3b8e59569..714587f24 100644
--- a/builder/virtualbox/iso/builder_test.go
+++ b/builder/virtualbox/iso/builder_test.go
@@ -83,7 +83,7 @@ func TestBuilderPrepare_DiskSize(t *testing.T) {
 	}
 
 	if b.config.DiskSize != 60000 {
-		t.Fatalf("bad size: %s", b.config.DiskSize)
+		t.Fatalf("bad size: %d", b.config.DiskSize)
 	}
 }